Miller, formally of Hartlepool, is a box-to-box midfielder with a keen eye for goal although he failed to hit the heights at the Stadium of Light following a 2005 move north from Portman Road.
The 28-year-old was released by The Black Cats and Brian Laws has already stated his interest in picking up the player on a free.
Laws told Sky Sports: "I have spoken to a number of players, and he is a player we have had talks with - particularly with his agent - but it's not gone further than that."
Simpson meanwhile is set to leave The Abbey Stadium following a 17-goal season in the Nationwide Conference.
Coventry